Create linked Metagov IDs on Discord login

[gigxz]

The Discord plugin should create/link Metagov accounts on login, like Slack does.

Add this back and test it out:

gateway/metagov/metagov/plugins/discord/handlers.py

Lines 225 to 232 in 2c0496d

	# TODO: add this back and test it. Where is 'external_id' coming from?
	# logger.debug(f"adding/updating linked account for {current_user['username']}")
	# result = inst.add_linked_account(
	# platform_identifier=current_user["id"],
	# external_id=external_id,
	# link_type=LinkType.OAUTH.value,
	# link_quality=LinkQuality.STRONG_CONFIRM.value,
	# )